Recently, the number of files managed by computers is increasing due to development and the widespread use of computers. Documents like reports, plans and contracts which were processed as papers in the old times, are now managed electronically using computers, and they are more differentiated for use in business. A total amount of electronic documents is on the rise continuously, and it grows still more as various mobile devices are used for document management.
However, a problem arises when users cannot find the file they want, because they cannot remember exactly the file's location or its name. The users may utilize file searching programs like a windows explorer or a finder but the problem is still there if they cannot recall exactly the file names or the folders storing the file. The reason is that the file searching programs compare the keywords inputted by users with attribute information when searching for the file, but the attribute information of the file is limited to a small amount and that makes the keywords that the users may input very limited. That is to say, the information saved as the attribute information about an electronic document is somewhat limited to a file creation date, a file modification date, a file name, a file size, a file editor, a file type and etc. and the file can be found by keywords related only to this information.